select userinfo.id, user_name, role, adm_regionid, region_name , create_timefrom userinfoleft join region on userinfo.adm_regionid = region.id
结果：
设置显示默认值：
select userinfo.id, user_name, role, adm_regionid, ifnull(region_name,0) as region_name, create_timefrom userinfoleft join region on userinfo.adm_regionid = region.id
即：如果region_name一列的值为空，则显示为0，结果为：